1. Field of the Invention
The invention relates, in general, to a color change valve arrangement for selectively connecting an applicator of a coating plant to a plurality of supply lines for coating material of different selected colors.
2. Description of the Related Art
Valve arrangements for selectively connecting an applicator of a coating plant to a plurality of supply lines for coating material of different selected colors, which are needed in coating plants for the production coating of work pieces such as vehicle bodies, are known from DE 198 36 604 and DE 198 46 073 and others. These color change valve arrangements, or color changers for short, make it possible to switch quickly from one color to another during painting operations in paint plants and consist mainly of a plurality of controllable paint valve assemblies that are distributed along a paint passage common to all of them. To adapt to the particular plant and the number of selectable colors, they are formed in modular fashion from individual modules (connector blocks, manifold blocks, control heads) that can be stacked in rows so that a variable number of connections for paint lines, which can subsequently be enlarged or reduced, can be implemented. In addition to the paint valves there are usually additional, similarly-constructed valves for purging media such as solvent and pulse air. The valve assemblies consist for their part of pin or needle valves, whose valve needles are pressed into the closed position by a pressure spring and are opened against its force by a pneumatically-activated piston drive. The valve needles of the valve assemblies disposed next to each other along the normally straight central passage are moved in parallel planes which lie perpendicular to the axis of the central passage to improve flow characteristics but can also be disposed at an angle (DE 198 46 073, WO 02/09886). To save space, color changers are also known which in place of the customary straight central passage contain a spiral groove at right angles to the longitudinal axis of the color change block (DE 43 39 301). This, however, less conducive to flow than a straight central passage.
From EP 1 205 256 it is further known to have permanent pilot control of the paint and purging agent valves, using a pressurized air line common to all valve assemblies, and to actuate them by added electronically controlled solenoid valves. This dispenses with the required control air lines found in the normally pneumatically-controlled color changers.
In principle, color changers of the category under consideration here are distinguished by considerable advantages such as freedom from dead space, good purge capability, little dead volume, small size, low weight, modular construction, small number of different parts, ease of installation, maintenance and repair, etc. They have consequently proved their worth in practice for a long time. The disadvantage with the known color changers is their length in the longitudinal direction of the common central passage to match the number of selectable colors. As a result, the known color changers are relatively poorly suited to installation in confined areas of coating equipment, as for example painting robots, and even less suited to installation in the atomizer itself mounted on these machines, which may be desirable for the reasons explained in the co-pending application filed concurrently herewith in the name of Stefano Giuliano, which is entitled Spraying Device for Serial Spraying of Work Pieces.
An object of the invention is, therefore, to reduce the length of the color changer in the longitudinal direction of the central passage common to the valve assemblies and in particular to reduce the size of the valve assemblies perpendicular to the needle axes to a minimum without thereby prejudicing the required sealing effect of the valve needle pressed against the valve seat.